Denver's performance-pay system for teachers has long been hailed as a model, in good part because it was jointly conceived and implemented by the school district and the local teachers' union. However, that collaborative spirit is now in jeopardy, with union and district leaders engaged in a protracted battle over proposed changes to the system. The two sides are expected to go to the negotiating table August 20 to sort out their differences, and have been meeting separately with mediators in the interim. However, the rift is wide enough that the union, in a recent newsletter, called on teachers to prepare for a strike if negotiations fall through. This article highlights the union's opposition to the district's proposed changes to Denver's ProComp or Professional Compensation Plan for teachers.